We have lots of "hard evidence" of global warming, like the rapid loss of glaciers, rising oceans, etc.
But we should not have spent a cent and I do not think we did in order to reduce the problem.
The correct means of reducing global warming is to burn less fossil fuel, which should save us money instead of costing anything.
That is easily done with smaller vehicles and more mass transit, which save money.
The fact the EPA went with Parts Per Million and encouraged larger vehicles, obviously was a Detroit fraud, not the fault of the tree huggers.